The present invention relates to the novel technique for dimerizing acrylonitrile to form the corresponding linear dimers, 1,4-dicyanobutane (adiponitrile) and 1,4-dicyanobutenes.
The catalytic dimerization of acrylonitrile is already known. For example, U.S. Pat. No. 3,671,569, the disclosure of which is incorporated herein by reference, teaches that 1,4-dicyanobutenes and adiponitrile can be made by heating acrylonitrile in the liquid phase in the presence of hydrogen and a catalyst comprising a ruthenium compound or complex. U.S. Pat. No. 3,790,617 and U.S. Pat. No. 3,729,498, the disclosures of which are also incorporated herein by reference, further teach that this reaction can be conducted in the vapor phase by employing ruthenium metal or a mixture of a solid ruthenium compound and another compound as the catalyst.
Each of these techniques has its own disadvantages. The liquid phase process is difficult because separation of the expensive liquid phase ruthenium catalyst from the liquid phase products and reactants is difficult. In the vapor phase process, selectivity and single pass yields of the desired linear dimers is low.
Accordingly, it is an object of the present invention to provide a new technique for dimerizing acrylonitrile to the corresponding linear dimers, adiponitrile, cis-1,4-dicyanobutene and trans-1,4-dicyanobutene, which employs a heterogeneous system, i.e. catalyst in a different state than products and reactants, and which provides the desired products with high selectivities and yields.